It has become increasingly common for farmers to ensile crops using biological additives. These commonly comprise enzymes designed to release sugars from cellulose, to promote the fermentation by naturally-occurring organisms, or microbial inoculants which use endogenous sugars, again to promote the production of lactic acid by fermentation. In some instances, a combination of the two technologies has been used.
Weinberg et al, Enzyme Microb. Technol. 12 (1990) 921-925, describe the simultaneous lactic acid fermentation and enzyme hydrolysis by cell wall-degrading enzymes, in order to recover protein from alfalfa. The preferred formulation contained mainly hemicellulases, cellulases and pectinases. It is hypothesised "that the synergistic action of enzymes and lactic acid bacteria removes a considerable portion of hemicellulose and other polysaccharides from the plant cell wall, increasing its permeability for cell content recovery."
Bolenz et al, Biological Wastes 33 (1990) 263-274, describe the use of pectinase/cellulase in order to solubilise the protein in water hyacinth. Lactofermentation is described as a "prerequisite for silage production" but requires the addition of sugar and the suppression of mould growth. Once again, the intention is to extract protein.
Willis et al, J. Animal Science 50 (2) (1980) 303-308, describe the addition of sodium hydroxide and enzymes to rice straw, in order to improve its nutritive value. The enzymes comprised hemicellulase, pectinase and .beta.-glycosidase. The data relating to ensiled materials indicate that sodium hydroxide increases, while the enzymes decrease, dry matter digestibility.
Jorgensen et al, "Enzyme Systems for Lignocellulose Degradation", ed. Coughlan, pub. Elsevier (1989) 347-355, describe the use of hemicellulase to produce fermentable sugars such as xylose, arabinose and glucose in ensiled material for use as animal feedstuff. Although it is suggested that cellulose degradation may weaken the structure of the grass and cause drainage from a silo, the recommended formulation comprises "a cellulose complex consisting of endo- and exo-activities and including .beta.-glucosidase (cellobiase)" in order to maximise the production of fermentable glucose and minimise structural disruption in the cell walls. The conclusion states that there is "continuing lack of knowledge about substrate composition, enzyme complexity and all of the other parameters crucial for occurrence of enzyme effect."
Commonwealth Agricultural Bureaux, Abstract 870701129, OG57-01979, reports that six enzyme preparations were tested on substrates including maize. It is suggested that enzyme formulations for degrading plant cell walls should be composed of hemocellulases and pectinases rather than cellulases.
GB-A-1591810 discloses the preservation of vegetables using a combination of bacteria and enzymes. The bacteria should be capable of both degrading higher carbohydrates into fermentable sugars and also of causing the fermentation of such sugars into lactic acid. The enzymes should be capable of breaking down carbohydrates, and in particular cellulose, starch and pentosans. Amylase, amyloglucosidase and hemicellulase are used, the latter defined as comprising galactomannase, pectinase, .beta.-glucanase, xylanase and cellulase.